Raingarden Maintenance: Plant Replacement And Establishment

December 23, 2014

As you may have read in our recent blog post ‘Green Streets for Blue Waters’, our two year project in partnership with the City of Bloomington just wrapped up. The project included the addition of 18 newly installed curb cut raingardens and a fabulous vegetated bio-swale. After installations were complete, we were charged with ensuring these new practices are maintained by residents so they continue looking great and functioning properly. When raingardens aren’t maintained they can fill with sediment, lose their ability to infiltrate water, get taken over by weedy species and lose their aesthetic appeal, which leads to poor public perception. It’s an issue everywhere raingardens are installed, so making sure homeowners have the tools they need to maintain their gardens is no small task!

To kick off our maintenance education in Bloomington, each participant had the opportunity to meet one on one with Metro Blooms designer and maintenance expert Andrew Novak. Our hope with these visits was to instill a sense of confidence and ownership in participants as they care for their new raingardens. Gardening can be a very rewarding experience, both physically and mentally, and good maintenance is the most important aspect for ensuring the longevity and success of each garden.

In addition to conducting one on one consultations, Metro Blooms provided two maintenance events for Bloomington residents who have participated in past City installation projects. The events included a tour of project sites in different stages of plant establishment. Each garden showcased various degrees of maintenance and illustrated the benefit of continued maintenance as plants grow towards maturity. The first event culminated in a learning-by-doing activity to engage participants in a “hands on” raingarden rehabilitation. Residents worked with Metro Blooms designers to weed and replant an existing garden and learned techniques for maintaining their own gardens. These maintenance events were a great opportunity for participants to identify common weeds and experience first-hand the importance of pulling invasive species before they grow too large for easy removal. Participants also learned about replanting, seed dispersal, and pruning shrubs.

Plant Identification and Replacement

One of the greatest challenges property owners face when maintaining their raingarden is identifying which plants are supposed to be there and which plants are weeds. To address this, each participant was given a copy of the planting plan for their garden. As plants grow throughout the next growing season, we encourage each participant to get to know the plants in their new garden. This knowledge is key to proper maintenance. Most raingardens in this project employ a small palette of 9-12 plant varieties to make it easier for participants to identify and work with the beneficial plants used in their garden. This also makes identifying and removing unwanted plants less of a chore.

Inevitably, some plants will die over time and need to be replaced. Each of the Bloomington raingardens was thoughtfully designed to offer visual interest with a variety of bloom times, and plants can certainly be replaced with the same variety. However, if you plan to use a different plant, it’s important to remember that plants are chosen for a raingarden according to their ability to thrive within the extreme wet and dry conditions that characterize these gardens.

Typically designers choose plants for raingardens that are best described as drought tolerant with various moisture tolerances. This is why we use native plants as much as possible. Native plants have evolved through time to respond to our soil conditions and weather patterns. The moisture tolerance necessary depends on the area of the garden the plant will be put in. There are three distinct “zones” in each raingarden: the edge, side slope, and basin. Edge species thrive in drier conditions where there will be no inundation. Some plants have a higher tolerance for wet soil conditions and can thrive in what are called mesic soils. These species are often used for the sloped sides of raingardens. Plant species used in the basin of a raingarden can handle temporary pooling of water during large rain events.

There are many references online to help with plant identification and selection. We suggest the Blue Thumb Plant Selector Tool. The plant selector will help participants learn about the plants in their garden and find replacement plants for the different zones within their raingarden. This will be an important facet to good maintenance, ensuring the longevity and ecological function of each garden.

Raingarden Establishment

You’ll often hear designers talk about the “establishment period” of a raingarden. This period is the first 2-3 years after the garden is installed when plants are reaching maturity. During this time, raingarden maintenance is crucial for the success of the garden and requires a few extra steps to ensure that plants thrive into maturity. These steps include:

Watering: During the first year of establishment it is important that the garden receives at least an inch of water each week. You can use a gauge of some sort to ensure the garden is receiving an adequate amount of water. A conventional rain gauge works, or simply use a container of some kind with a one inch marking on the side. Substantial water throughout the first season will ensure that strong healthy roots develop. If the garden was planted in the fall, consider the first year of growth to be starting with the following spring. After the first season, plants will be more self-sufficient and you won’t need to water as much. By the third year, raingarden plants should need almost no supplemental irrigation and should thrive with natural precipitation.

Weeding: Many weeds respond well to the disturbance that occurred during excavation and will try to invade the substantial space between small newly planted plants. The secret to weeding is to catch weeds when they are small. Once established, many weeds are a major chore to remove. Check out photos of some common garden weeds here. After three years or so, plants should be reaching maturity. With maturity comes height and width of plant foliage which acts like living mulch. Mature plants are better at holding their own against invading weeds.

After establishment, raingardens require little maintenance. But remember, raingardens are LOW maintenance, not no maintenance. Periodic weeding and plant replacement will continue to be necessary, even past the establishment period. However, if gardeners make a little extra effort during the establishment period, they will be rewarded with healthy, vigorous, resilient plants that will thrive for many years with relatively low maintenance.